Generally, the game does that for you. There's zones for certain levels. Once you get a breadcrumb quest to that area (for instance, to the jade forest when you hit 85) you get sent to the right starting hub.

Back inn vanilla and TBC I did use lvling guide myself (The now Infamous James lvling guide), and it helped alot, cause the questes wasen't always obvious on what to do, or the questes were hidden or not chained together to well.

I'm going to disagree with all of the above OP, and recommend Dugi's ultimate wow guide. I've used it for many years now, and I must say it's unbeatable. (I have tested Zygor's and James guides but neither are as lightweight and user freindly as Dugi's IMO) Yes, Dugi's guide costs a bit, but it really lets you know what you're doing. Theres nothing more horrible then doing a quest, running back to a hub, seeing that you've missed a quest for the same area, and having to go back and kill the same mobs again just for this different quest :/

quite easy to point out a lvling guide.. or guidelines.. heres what i normally do
85: do every quest in the jade forest.. and run each random mop heroic once for the quest exp this should get u near 86-86.5
86.5: run to the valley of the 4 winds and do all the quests down to halfhill.. get the farming quests started for gina and then head over to stoneplow and the hidden master quest. u should be near 87. skip the safari quests and karasang wilds as they are normally a waste of time.
87: kun lai summit. u can do every quest here except the Winter's blossom, Kota Base Camp and u should be 88 easily. you are only here for 1 lvl so it wont be that long.
88: venture into townlong steppes and complete almost every quest here, you can skip Swamprushes if you choose but be sure to quest till 89. once you are 89 just head into the Brewgardens to gain the flightpath for the Serpent's spine.
89: do every quest in the dreadwastes.. literally. depending on the time of day the Klaxxi usually will have dailys to offer as well, be sure to do them as they will reward rep valor and a ton of experience. if you had the badge from being revered you will easily get revered as well leaving a few more 280,000 exp quests. this will get you to 90 near the end of the dread wastes.
i usually ding 90 from 2 days of questing from 85 so this method tends to work for me.